Prior art methods for consolidating a powder, such as nickel, titanium, or cobalt-base superalloys, generally consist of the steps of filling a thin-walled container with the powder, placing the container in an autoclave, raising the temperature of the autoclave to a predetermined temperature, and then raising the pressure to a predetermined pressure to cause compaction. During this process, the powder is first subjected to a high temperature and then the pressure is raised to the predetermined pressure at which the powder will become a compact, the raising of the pressure requiring a long time period.
Problems can be experienced using this prior method. First, the container in which the powder is compacted may have a shape such that, as the pressure is applied to the already heated container and powder, certain areas of the container may move inwardly prior to other areas thereby resulting in a compact of a shape which is other than the desired final shape. In other words, when first heating the container to the temperature necessary for compaction and they applying pressure to the container, it is frequently impossible to obtain the desired shape because of the uneven inward movement of the various portions of the container surrounding the powder. Secondly, when the powder is at the high compaction temperature for the very long time required to raise the pressure to that required for compaction, there is time for dissolved carbon to be diffused to the surfaces of the powder particles. This results in undesirable boundaries between the particles in the densified compact or article.
An example of a prior art process is disclosed in the U.S. Pat. No. 3,954,419 to Kaufman et al, granted on May 4, 1976. The Kaufman et al patent discloses a cycle for compacting powder metal under heat and pressure by first heating the powder metal in a graphite die to about 1900.degree. to 2100.degree. F. then applying a pressure of about 2700 to 3300 psi, followed by heating the material to about 2600.degree. to 2700.degree. F. while the pressure is maintained constant. In other words, the container or die is heated to a high intermediate initial temperature, a pressure is exerted on the powder within the container, and then the container is further heated to a temperature while the initial pressure is maintained.